This invention relates to novel olefin polymer compositions, to a process for making foamed or expanded articles therefrom and to foams of these olefin polymer compositions which are characterized, in fresh or non-fully cured form, by improved elevated temperature distortion characteristics.
It is common practice to make closed-cell ethylenic polymer foams by an extrusion foaming process comprising the steps of heat plastifying a thermoplastic ethylenic polymer; admixing the heat plastified polymer under pressure with a volatile material such as 1,2-dichlorotetrafluoroethane and passing the resulting mixture through a die opening or shaping orifice into a zone of lower pressure to vaporize the volatile constituent and form a cellular structure which upon cooling forms the corresponding cellular solid ethylenic polymer foam. However, the development of a viable commercial extrusion foaming process--especially for relatively low density foams of lower olefin polymers--requires balancing a number of different (and sometimes competing) business and technical requirements. Accordingly, much of the extrusion foaming technology is empirical, based upon experience and directed to very specific materials and processes to produce specific commercial products.
One of the requirements for acceptable olefin polymer foam products of growing importance is the elevated temperature distortion characteristics of such products in fresh or partially cured form (i.e., the dimensional stability at elevated temperature of the foam prior to sufficient storage or aging to permit substantially complete replacement of the original blowing agent within the cellular structure of the foam with air). Such characteristic is of growing importance because (a) the elevated temperature distortion characteristics of relatively fresh olefin polymer foams are significantly dependent upon the particular ingredients (e.g., blowing agent, additives, etc.) employed in its preparation; (b) warehousing costs, storage space factors, and/or other considerations oftentimes mandate shipment of the olefin polymer foam products from the manufacturing facility prior to the time that they become fully cured; and (c) such partially cured foam products may, during transport, in enclosed vehicles particularly in warm climates or during hot weather, be subjected to prolonged exposure at relatively high temperatures. Moreover, this concern is even further aggravated by the recent trend toward the use of various stability control agents which provide improved ambient temperature dimensional stability with a wider variety of blowing agents, but which unfortunately also generally lengthen the time required for the olefin polymer foam product to reach its so-called fully cured state.
In view of the foregoing, it is an object of this invention to provide olefin polymer foams having, in fresh foam form, improved elevated temperature distortion properties as well as to provide olefin polymer compositions which are expandable to form such improved polymer foams. Another object of this invention is to provide a means to improve the dimensional stability of fresh olefin polymer foams at elevated temperatures. In addition, it is a particular object of the instant invention to provide olefin polymer foams which, in fresh foam form, have increased heat distortion temperatures and/or which, in fresh foam form, require reduced aging time at ambient temperature to reach a state at which such foam will not shrink more than five percent in volume during prolonged exposure to an elevated temperature of up to about 150.degree. F. Other objects and advantages of the present invention will be apparent from the description thereof which follows.